Steering system with automatic increase of rate time

ABSTRACT

An automotive steering system including means for producing a commanded course change which is the difference between the preset course and a desired course and including an operational unit capable of accomplishing proportional and differential control and having rate feedback and in which a position feedback signal is applied to the input of the operational unit through a circuit which has a dead zone feature such that when the position feedback signal exceeds a predetermined level the time constant of the operational unit is changes so as to prevent over-shoot of the autopilot when making large corrections.

0 United States Patent 1151 3,656,043 Kawada et al. [45] Apr. 11, 1972[54] STEERING SYSTEM WITH [56] References Cited gg INCREASE 0F RATEUNITED STATES PATENTS 2,939,066 5/1960 Crenshaw ..318/6l7 [72]Inventors: Shin-ichi Kawada, Yokohama; Yoichi 3,505,577 4/1970l-iirokawa ....3l8/561 Hirokawa, Kamakura; Isao Masuzawa, 3,296,5201/1967 'Grifiith ....307/237 Tokyo, all of Japan 3,028,534 4/ 1962Chilton ....3 1 8/617 [73] Assignee: Kabushikikaisha Tokyo KeikaSeizosho ggg g (Tokyo Keiki Seizosho Co. Ltd.) Tokyo a a J I 3,270,3448/1966 Righton ....318/6l7 3,299,293 l/l967 Knapp Ziller ....30?/261[22] Filed: Feb. 2, 1970 3,431,475 4/1969 Wesner ..318/624 APPI'NO':L631 PrirharyExaminer-Felix D. Gruber Attorney-Hill, Sherman, Meroni,Gross & Simpson [30] Foreign Application Priority Data [57] ABSTRACTFeb. 8, 1969 Japan ..44/9388- Y v Feb. 8, 1969 Japan ..44/9389 Anautomoflvesteermgsystem mcludmg meansforproducms a commanded coursechange which is the difference between 52 us. (:1 ..3l8/588, 318/610,318/621, the Preset Course and a desired course and including an p235/1501, 235/1502, 235/183, 328/171 tional unit capable ofaccomplishing proportional and dif- 51 1 1111. C1. .0051 11/14 ferehtialcontrol and having rate feedback and in which a p [58] Field of Search..235/183, 150.2, 150.22-15026, tioh feedback Signal is applied to theinput of the Operational unit through a circuit which has a dead zonefeature such that when the position feedback signal exceeds apredetermined 621, 624 I level the time constant of the operational unitis changes so as to prevent over-shoot of the autopilot when makinglarge corrections.

5 Claims, 9 Drawing Figures A R :75 6 a N 1 I T LI l/ Z5 1 -i I F I E,6R2 g y /1, 3 i i W6 *1? 9 A 1. A v l 1 I Patented April 11, 1972 3Sheets-Sheet 2 Patented April 11, 1972 3 Sheets-Sheet 5 0 w mm wwwmm 14AK ow Ks m n v W Hm 5v// 1. STEERING SYSTEM WITH AUTOMATIC INCREASE OFRATE TIME BACKGROUND OF THE INVENTION l. Field of the Invention Thisinvention relates to an automatic steering system, and more particularlyto a marine automatic steering system which is of particular utilitywhen employed in giant vessels such as super tankers.

2. Description of the Prior Art Marine automatic steering devices havebeen used for a long time. Automatic steering devices for giant vesselsnow in use usually perform proportional and differential operations.With the use of such automatic steering devices, giant vessels can beaccurately controlled to maintain set courses but such equipment doesnot control, the vessels accurately to a newlyset course. When giantvessels deviate from their set courses dangers such as collision withother ships, or reefs or the like arise. Such a deviation from thecourse is caused mainly by the steady-state turning characteristic ofthe ship. When turning a giant vessel of about 100,000 to 400,000 deadweight tons (DWT) (almost all of which are oil tankers), even if therudder angle is small, the steady-state turning angular velocity of theship is much higher than would be expected and the relationship betweenthe steady-state turning angular velocity and the rudder angle isnon-linear.

SUMMARY OF THE INVENTION One object of this invention is to provide amarine automatic steering system which is capable of effecting usualproportional and differential operations for maintaining a set course ofa ship and automatically intensifying the rate operation in the case ofan automatic course change thereby to ensure prevention of over-shoot ofthe ship from a newly-set course.

Another object of this invention is to provide a marine automaticsteering system which prevents deviation of the above giant vessel fromits course in the event of an automatic course change so as to preventcollisions or like accidents.

Other objects, features and advantages of this invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing thesteady-state turning characteristic of a giant vessel which is oneexample of an object to be controlled by the system of this invention;

FIG. 2 is a block diagram of one example of an automatic steeringsystem, for explaining the principles of the present invention;

FIG. 3 is a connection diagram showing one embodiment of this invention;

FIGS. 4 to 8 are connection diagrams illustrating modified forms of thisinvention; and

FIG. 9 is a circuit diagram showing a modification of the principal partof the examples of this invention illustrated in FIGS. 3 to 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1 adescription will be given first of the turning characteristics of a hugevessel so as to facilitate a better understanding of the principles ofthis invention. Generally, the relation between rudder angle 6 and theturning angular velocity of the giant vessel obtained by spiral orreverse spiral tests, has a characteristic as indicated by the curve ain FIG. 1. The turning angular velocity Ois representative of a valuewhen the ship is turning under steady-state conditions (while the shipis turning with a constant radius under steady-state conditions). Whenthe course of a giant vessel, is changed automatically and the angle ofthe course change is large the vessel will vturn at substantially thesteady-state rate before reaching the newly-set course, and the turningangular velocity 0 is indicated by curve a in FIG. 1. When a coursechange of less than several degrees or when a set course is maintainedwith an automatic steering system, the ship does not turn atsteady-state rate and the turning velocity of the ship is suprisinglylow. It is thought that the ship is subject to a transient phenomenon inthe latter case. Thus, the turning characteristics of the ship aredifferent in the former and latter cases. Accordingly, when the courseis changed by a large angle by the automatic steering system in a systemin which the rate time is set for suitable automatic maintenance of theset course, the ship will over-shoot the newly-set course by a largeamount. Especially is this true as to a ship which has such hysteresisbetween 6 and 8 as indicated by the curve b in FIG. 1. If the rate timeis selected to be suitable for large course change, the rate time willbe too long for the maintenance of the set course and the steeringdevice will be too sensitive and will over-respond to externaldisturbances such as waves, winds and gimballing errors produced by acompass device. These factors will cause an unnecessary increase in thenumber of steering operations and hence result in abuse of the steeringdevice.

To avoid this, the rate time is automatically varied with a deviation A9(between a set source 0i and the actual ships heading 0) and the turningangular velocity 0. It is not practical to continuously vary the ratetime as a function of the deviation A0 and the turning angular velocity0, because such device is too complicated and expensive.

The present invention comprises a system in which the rate time is T,and T, Ta, respectively, under the conditions of the following equations(1) and (2) and the invention resides in a system in which it ispossible to readily, positively and cheaply achieve the variations ofthe rate time in a non-linear manner.

|A6 Tm K1. (2)

where T is'a constant and K is a value determined by the ship and hersailing conditions.

A description will be given of one example of determination of the aboveconstants T and K Assuming that K is 5 that T is 30 seconds and that theturning angular velocity 6 of a giant vessel is 0. 1 per second, T O is3 and when A0 is about 2, I A0 T OI is more than (2 3) 5, satisfying theequation (2). Accordingly, the desired rate time is T, Ta in this case.

When the ship advancesin a straight course, that is, when the turningangular velocity 6 is substantially Zero, the above numerical valuessatisfies the equation (1), so that the rate time fulfills the equationl and is T In all of the cases where the ship has begun steady-stateturning and her turning angular velocity 0 has reached a large value incomparison with the amount of the rudder angle 8 as represented by thecurves a or b in FIG. 1, and where the deviation A0 has been increasedby varying the set course (ii in the event of an automatic course changeand where both the turning angular velocity 0 and the deviation A6 aregreat, the above equation (2) is satisfied and the rate timeof theautomatic steering system increases up to T, Ta which will preventover-shooting of the ship of the commanded course.

FIG. 2 is an example of the automatic steering system which effectsproportional and differential operations; (ii is representative of a setcourse of a ship, and 0 the ships actual heading which is detected by agyrocompass or magnetic compass. The set course 0i and the actual shipsheading 0 are compared with each other in an adder 1 and the resultingdeviation A0- between them is converted by an angular signal generator 2into a DC electric voltage E at line 3. Since mechanisms for generatingthe set course 6i and the actual ships heading 0 and adding them arewell known, a detailed description of them will be given. In ships usinga gyrocompass, a step motor or a synchro is usually employed fortransmitting the actual ships heading 6 to the automatic steeringdevice. In a typical system the set course (ii is given by a dial cardand graduations and a shaft for transmitting the angle (ii is coupledthrough a difgenerator 2 may also comprise a synchro and a demodulator.

The voltage fed to the line 3 is proportional to the deviation orheading error, that is, i 0 A0. In FIG. 2 reference numeral 4 indicatesgenerally an operational unit which consists of resistors R R R Rf acapacitor C and an operational amplifier 5 having a gain of aboutReference numeral 7 designates a controller, which is supplied with theoutput of the operational unit 4 through a line 6. The controller 7controls a power unit 8 and may be, for example, an amplifier performingthe function of a relay and a solenoid value. The

power unit 8 may be, for instance, a hydraulic power unit consisting ofa piston and a cylinder. Since the devices 7 and 8 are not directlyrelated to this invention, a detailed description will not be given. Theunit 8 also may be a motor-type power unit.

A rudder order angle 8 is produced by the power unit 8 and analogcomputer techniques, so that if the input voltage from the resistor Rf,is taken as Vx, the following equation is obtained.

With E =k A0, the voltage Vx is derived from the above 10 equation asfollows:

is simultaneously converted by a signal converter 9 into an electricsignal and is then fed to the resistor Rf of the operational unit 4through a line 10 and a circuit 11, thereafter being applied to theinput side of the operational amplifier 5. The signal converter 9, theline 10, the circuit 11 and the resistor Rf constitute a feedback loop.

A brief description will be given of the operation of the automaticsteering device shown in FIG. 2. If a difference exists between the setcourse 6i and the actual ships heading 6, a voltage IE is fed to theline 3 through the angular signal generator 2 which is proportional tothe deviation A0. The voltage may be assumed to be k,A6, and it isapplied as an input to the operational unit 4. The operational unit 4 isconstructed by the usual analog computer techniques, and a signalproportional to the deviation A0 and a signal proportional to rate areboth transmitted through the capacitor C and the resistor R and areadded together and applied to an input terminal j of the operationalamplifier 5. Further, the rudder position signal is transmitted throughthe resistor Rf and is also added to the above signals at point j andthen applied to the input of the operational amplifier 5. The outputsignal of the operational amplifier 5 is applied as a negative feedbacksignal to the input terminal j through the resistor R balancing theinput signal. Since the gain of the amplifier 5 is very high, thepotential at the point j is normally maintained at zero and the output Eof the amplifier 5 is exactly proportional to the difference between theinput transmitted through the elements R,, R and C and the rudder anglesignal through the resistor Rf When the voltage E is substantially zero,the controller 7 remains in its neutral position. However, when E is notzero, the controller 7 controls and drives the power unit 8 in adirection depending on the polarity until the voltage E becomes zero,thus producing the rudder angle 6. Therefore, if the circuit 11 consistsof only a resistor, the operational amplitier 5, the controller 7 andthe power unit 8 operate in such a manner that the proportional anddifferential signals of the deviation A0 applied to the point j and thesignal proportional to the rudder angle applied to the point j throughthe signal converter 9, the circuit 11 and the resistor Rf are alwaysequal to but opposite in polarity to each other. Also the resultingrudder angle 6 is always proportional not only to the deviation A0 butalso to its rate of change. Accordingly, the auto- (I S) A0 (4) Thefirst tenn in the bracket of the equation (4) indicates that the voltageVx is proportional to the deviation A0 and the second term in thebracket indicates that the voltage Vx is in proportional to the ratevalue of the deviation A9. The denominator R CS l of the second term inthe bracket shows that the rate value is equivalent to a valuetransmitted through a filter having a time constant R C. Accordingly, ifthe automatic steering system is designed to increase its rate time onlywhen the voltage Vx exceeds a certain value Vc, the rate operationincreases under the condition of the equation (2), thus attaining theobject of this invention. A comparison of equations (2) and (4) showsthat the constant T corresponds to R C.

FIG. 3 illustrates one example of this invention as applied to theautomatic steering system of FIG. 2. In FIG. 3 the same referencenumerals as those in FIG. 2 indicate the same elements and only theoperational unit 4 and the feedback circuit 11 of the system shown inFIG. 2 are illustrated. In the present example the operational unit 4 isidentical to the one shown in FIG. 2. The portion indicated by thebroken line corresponds ,to the circuit 11 of FIG. 2 and consists of aresistor Rf a capacitor Ca and a pair of Zener diodes Dz. Which areconnected in reverse directions to constitute a dead-zone element. Ifthe gain of the signal converter 9 is taken as k in this case, thevoltage E applied to the line 10 is expressed as k 8. If, now, the Zenervoltage is taken as Vc, when Vx Vc, the capacitor Ca cannot be suppliedwith current because it is blocked by the Zener diodes, with the resultthat only the resistor Rfg transmits the signal of the rudder angle 6 topermit the proportional and differential operations of the automaticsteering system as previously described in connection with the exampleof FIG. 2. In this case, the voltage at the point j is zero (because theelements 5, 7 and 8 operate the rudder in a manner to hold the voltageat the point j zero in the example of FIG. 2), so that the transferfunction of the automatic steering system of this example is given bythe following equation.

It appears from equation (5) that the rudder angle 8 varies with theproportional and differential values of the deviation A6 and that therate time is R C.

WhenlVxl exceedsthe Zener voltageyc, the capacitor Ca begins to drawcharging current which flows through the resistor Rf to cause a voltagedrop thereacross, so that the voltage applied to the resistor Rf isdelayed in phase behind that in the case where the capacitor Ca is notcharging. The transfer function of the automatic steering system can beapproximately given by the following equation when the capacitor Ca isin operation.

RIC

Rgcs +1 Therefore,

A comparison of the equation (7) with the equation (5) will show thefollowing facts. When lVx I exceeds the Zener voltage Vc, the rate timeincreases by Rf Rf Ca/(Rf Rf by. which the object of this invention isattained and also the term of S of the equation (2), that is, theangular acceleration control is added to the automatic steering system,thus further assuring that the ship does not over-shoot during anautomatic course change.

In accordance with the method above described with FIG. 3, by selectingR C to be a value suitable for the maintenance of the set course and byselecting Rf Rf Ca/(Rf Rf to prevent over-shooting of the ship duringautomatic course change, a highly precise control for maintenance of theset course can be achieved with an appropriate number of steeringoperations and, further, the automatic course change can be controlledso that the ship will not over-shoot. This is due to the rate having along, rate time and further including angular acceleration control.Further, since this system requires only the capacitor Ca and the Zenerdiodes D2 in addition to the elements of the example of FIG. 2, theconstruction of the automatic steering device is simple and economical.Also K for determining the conditions of the equation (2) can be easilyset to an optimum value by selecting the Zener diodes having the desiredvoltage Vc.

FIGS. 4 to 8, inclusive, illustrate modified forms of the presentinvention respectively, in which the same reference numerals as those inthe foregoing example indicate the same elements.

The example depicted in FIG. 4 is different from that of FIG. 3 in theconstruction of the operational unit 4. Namely,

in this example, the rudder angle signal transmitted through theresistor Rf is applied not to the input of the operational amplifier 5but to a point P on its output side. Further, the feedback resistor ofthe amplifier 5 is made up of resistors R and R and a series circuitconsisting of the capacitor Ca and the Zener diodes D2, which areconnected between the connection point of the resistors R and R andground. If the voltage at the connection point of the resistors R-, andR is taken as Vx, the following equation is given because the potentialat the point j is equal to zero as in the example of From a comparisonof the above equation (8) with that (3) it appears that the voltage Vxis the same as that obtainable when the resistor Rf, is substituted withR in the equation (4) and that the rate time is increased by theoperation of the capacitor Ca depending upon whether I Vxl exceeds theZener voltage Vc as in the example of FIG. 3. Therefore, it will beunderstood that the example of FIG. 4 is exactly equivalent to that ofFIG. 3 and that the object of this invention can be similarly attainedwith this circuit.

In FIG. 5 there is depicted another modification of this invention, inwhich the capacitor C and the resistor R on the input side of theoperational amplifier 5 in the example of FIG. 3 have been incorporatedin the feedback loop. The resistor Rf is divided into two resistors Rfand Rf and a series circuit consisting of the capacitor C and theresistor R is inserted between the connection point between theresistors Rf and Rf and ground. The present example is also equivalentto that of FIG. 3. In this case the rate time in the case where lVxl Vcand the capacitor Ca is inoperative is the same as that in the exampleof FIG. 3 except the time constant is defined by Rf Rf C(Rf Rf Althoughthis will not be proved for the sake of brevity, it can be readilyprovided by calculation methods using usual analog computer circuits.

FIG. 6 shows a further example of this invention, in which the ratecircuit in the example of FIG. 5 has been mounted in to the feedbackloop of the operational amplifier 5. The resistor R in FIG. 3 is dividedinto three resistors R R and R and the series circuit consisting of thecapacitor C and the resistor R is connected between the connection pointof the resistors R and R and ground and another series circuitconsisting of the capacitor Ca and Zener diodes Dz, D2 is insertedbetween the connection point of the resistors R and R and ground. Theother arrangements are substantially the same as those of the circuit ofFIG. 3 and this example is also equivalent to that of FIG. 3.

In another modified form of this invention illustrated in FIG. 7 acapacitor Cf is additionally inserted between the resistor Rf and theline 10, and non-linear rate operation is achieved in an automaticsteering system in which differential, proportional and integraloperations are effected.

FIG. 8 illustrates still another modification of this invention, inwhich the capacitor Cf is inserted between the resistors R and R shownin FIG. 4 thereby to achieve a non-linear rate operation in theautomatic steering system effecting the differential, proportional andintegral operations, as in the example of FIG. 7.

It will be seen from the equations (3) and (4) that the nonlinear rateoperation can be effectively accomplished and the capacitor Cf in theexamples of FIGS. 7 and 8 does not degradate such operation. The reasonis that substantial equality of the input terminal voltage of theoperational amplifier 5 to zero is independent of the circuit 11 andthat the equation (3) is not affected by the presence of the capacitorCf in connection with the circuit 11. Accordingly, in the examples ofFIGS. 7 and 8, the rate time can be made longer when lVxl exceeds theZener voltage Vc as in the example of FIG. 3.

The present invention described above resides in the automatic steeringsystem which has the rate time T under the condition expressed by theequation (1) and the rate time T, Ta under the condition given by theequation (2).

The foregoing examples employ the operational amplifier 5 but thisamplifier may be replaced with any other similar means, so long as themeans has high gain. In the embodiments of, for example, FIGS. 3, 5 and7, if the controller (indicated by 7 in FIG. 2) has incorporated thereina highly sensitive amplifier, it is possible to obtain an automaticsteering system in which the operational amplifier 5 is omitted and thepoint j is connected directly to one input of the amplifier incorporatedin the controller 7 but which carries out the same operations as thosepreviously described with FIG. 3.

Further, the means for providing the reference voltage Vc is not limitedspecifically to Zener diodes but may be in the form of any kind of adead-zone element or circuit. FIG. 9 illustrates one example, in whichno Zener diodes are used but instead conventional diodes D are connectedin opposition to each other and their connection point q is connected toone electrode of the capacitor Ca and a variable resistor Rx is insertedbetween the other ends of the diodes D. A series circuit consisting ofresistors Rc and Re 2 is connected to both ends of the variable resistorRx and the connection point of the both resistors Rc, and RC2 isgrounded. A voltage is applied from a DC power source E through suitableresistors Re and Re, to both ends of the variable resistor Rx of thecircuit connected as above described, thereby to suitably adjust thevalue of the variable resistor Rx, by which a reference voltagecorresponding to the Zener voltage can be obtained as desired.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thisinvention.

We claim as our invention:

1. An automatic steering system comprising:

a power unit;

a controller for controlling said power unit;

a signal converter for converting the output of said power unit to acorresponding electric signal;

an angular signal generator for generating an electric signalcorresponding to the difference between an actual ships heading and aset course; and

an operational unit for efiecting at least proportional and differentialoperations, said operational unit having a first circuit for providing afirst rate time of said differential operation and an amplifier;

the improvement comprising a second circuit consisting of a seriescircuit of a capacitor and a non-linear element, one end of said seriescircuit being connected to ground and the other end of said seriescircuit connected through a resistor to the input terminal of saidamplifier of said operational unit, whereby when voltage across saidnonlinear element exceeds a predetermined voltage, another rate time isobtained because said capacitor of said series circuit is added to saidfirst rate time of said first circuit to automatically increase ratetime of said automatic steering system. 2. An automatic steering systemas claimed in claim 1 wherein the second circuit is connected to theoutput side of said signal converter.

3. An automatic steering system as claimed in claim 1 wherein saidamplifier has a feedback circuit and said second circuit being connectedto said feedback circuit of said amplitier.

4. An automatic steering system as claimed in claim 1 wherein saidnon-linear element consists of a pair of Zener diodes mama! t ea the nwe e ne i y 5. An automatic steering system as claimed in claim 1wherein said non-linear element consists of a pair of diodes, a bias DCelectric power source and a variable resistor, whereby the predeterminedvoltage applied to said pair of diodes is varied.

1. An automatic steering system comprising: a power unit; a controllerfor controlling said power unit; a signal converter for converting theoutput of said power unit to a corresponding electric signal; an angularsignal generator for generating an electric signal corresponding to thedifference between an actual ship''s heading and a set course; and anoperational unit for effecting at least proportional and differentialoperations, said operational unit having a first circuit for providing afirst rate time of said differential operation and an amplifier; theimprovement comprising a second circuit consisting of a series circuitof a capacitor and a non-linear element, one end of said series circuitbeing connected to ground and the other end of said series circuitconnected through a resistor to the input terminal of said amplifier ofsaid operational unit, whereby when voltage across said non-linearelement exceeds a predetermined voltage, another rate time is obtainedbecause said capacitor of said series circuit is added to said firstrate time of said first circuit to automatically increase rate time ofsaid automatic steering system.
 2. An automatic steering system asclaimed in claim 1 wherein the second circuit is connected to the outputside of said signal converter.
 3. An automatic steering system asclaimed in claim 1 wherein said amplifier has a feedback circuit andsaid second circuit being connected to said feedback circuit of saidamplifier.
 4. An automatic steering system as claimed in claim 1 whereinsaid non-linear element consists of a pair of Zener diodes connected toeach other in reverse polarity.
 5. An automatic steering system asclaimed in claim 1 wheRein said non-linear element consists of a pair ofdiodes, a bias DC electric power source and a variable resistor, wherebythe predetermined voltage applied to said pair of diodes is varied.